Transcript Chapter 1: Animal Agriculture

Chapter 16: Egg Laying
• Chapter overview:
– Chapter 16 reviews the reproductive anatomy
of the bird and the physiology of egg laying,
including:
• structure and production of the egg
• anatomy of male and female bird
• factors affecting egg laying
Parts of the Egg:
• Shell - produced in the uterus
• Shell membranes - produced in the isthmus
• Albumen (white) - produced in the
magnum
• Yolk (ovum) - produced in the ovary
• Germinal disk - chromosome container on
the yolk
Egg Shell:
• Two main layers
– Composed of calcium carbonate
– Porous
– Translucent when laid; becomes opaque when
dry
– Covered by a thin film called cuticle which
tends to seal the pores
Shell Membranes:
• Two membranes are located just inside the
shell and surrounding the albumen
– Membranes are bonded together except at the
blunt end, or “air cell” end
– With time and evaporation the air cell forms by
the membranes pulling apart
The Egg White:
• The egg white (albumen) is high in protein
and water and has four principal layers:
–
–
–
–
Outer thin white
Thick white
Inner thin white
Thick white surrounding yolk; twisted into a
rope-like structure called the chalaza on
opposite sides of the yolk
The Egg Yolk:
• The egg yolk (ovum) is suspended in the
center of the egg by the chalaza and is:
– High in fat and water
– Arranged in alternating light and dark layers
– Contained in a thin yolk sac called a vitelline
membrane
– The location of the chromosomes in a germ cell
in a tiny area (“spot”) on its surface
Weight of Selected Bird Eggs, g:
Species:
Weight, g:
Ostrich
Goose
Turkey
Duck
Chicken
Pheasant
1,400
200
85
80
58
32
Incubation,
days:
42
28
28
30
21
24
Anatomy of the Avian Male:
• Testes - paired; located in the abdominal
cavity near the kidneys; sperm of the avian
survive at internal body temperature
• Vas deferens - paired; convey sperm
outside the body during mating
• Cloaca - terminus of the digestive and
urinary tract, also receives the vas deferens
• Vent - external opening of the cloaca
Anatomy of the Avian Female:
• Ovary - single; in chickens the right ovary
regresses in early life
• Stigma line - nonvascular suture line on
the developing follicle that ruptures to
release the ovum
• Infundibulum - funnel-like structure that
receives the ovum and guides it to the
remainder of the oviduct; site of fertilization
Anatomy of the Avian Female:
• Oviduct - single; anatomically divided into
several distinct areas:
–
–
–
–
Magnum: adds albumen
Isthmus: adds shell membranes
Uterus: adds shell; rotation creates chalaza
Vagina: prepares egg for laying (oviposition)
• Cloaca - terminus of the digestive tract; egg
passes through by inversion of the vagina
Hormones and Egg Laying:
• Follicle stimulating hormone (FSH) stimulates growth of ovarian follicles;
source: anterior pituitary
• Luteinizing hormone (LH) - causes
ovulation; source: anterior pituitary
• Parathyroid hormone - maintains blood
calcium balance for egg shell formation;
source: parathyroid glands
Hormones and Egg Laying:
• Thyroid hormone - influences molting and
seasonal changes in egg laying; source:
thyroid gland
• Oxytocin - causes oviposition and laying;
source: posterior pituitary
• Prolactin - causes manifestation of
maternal instincts; source: anterior pituitary
Factors Affecting Egg Laying:
• Age at sexual maturity - commercial egg
laying is optimized by managing hens to
begin production at about 20 weeks of age
• Light pattern - optimize production with
14-18 hours of (artificial) day length
• Removal of eggs from the nest - removal
increases rate of egg laying
Intensity of Egg Laying (Chickens):
• Interval between ovulations is 24-26 hours
• “Clutch”- an uninterrupted series of laying
days of 10-14 days is desired; inheritable
• Laying begins at 18 to 20 weeks of age
• Peak production (90 percent laying per day)
is reached at about 30 weeks of age
• Laying period is typically 12 to 14 months
Molting and Recycling:
• Molting - shedding and replacing of feathers
– A rest period to rebuild hens that are to be
recycled
– Reduce light, feed, and water
– Requires a period of 6 to 8 weeks to rebuild
• Recycling - allowing hens a second laying
cycle
– Shorter production period, but larger eggs
Factors Affecting Egg Size:
• Genetics - egg weight is highly heritable
• Age of bird - older birds lay larger eggs,
therefore recycling can be an advantage
• Size of bird - larger hens usually lay larger
eggs
• Environment - heat stress reduces egg size
• Nutrition - balanced diets maximize
production and shell strength